In some conventionally used magnetic display panels, a magnetic material (magnetic particle) of a fine particle is dispersed in a dispersion liquid, and a magnet is operated through one surface in which the above-mentioned magnetic particle is allowed to migrate so as to form an image on the magnetic display panel. When unnecessary, the magnet is operated from an opposite side so as to settle the above-mentioned magnetic particle and eliminate the image.
Further, a magnetic display panel which carries out display by reversing a display magnetic particle is proposed in Japanese Patent Publication No. S59-32796. This magnetic display panel employs a dispersion liquid in which a magnetic particle having a specific remnant magnetization moment and a specific coercive force is dispersed in a dispersion medium, and which has a specific yield value.
Furthermore, as described in Japanese Laid-open Patent No. 2001-201772, the present applicant previously proposed a magnetic material inverting display panel in which a liquid dispersion, having a yield value, whose principal components are a dispersion medium, a thickener, and magnetic display materials, in fine particle form, whose poles are differently colored, is supported by a supporting member, wherein a total area of magnetic S-pole surfaces or magnetic N-pole surfaces of the above-mentioned magnetic display materials in fine particle form is from 60 to 500% of a display screen area of the display panel. This magnetic material inverting display panel has a good contrast, provides clear display, and an outstanding effect. However, when the panel is placed vertically and display and elimination are repeated, there is a disadvantage that magnetic display materials settle and cohere gradually, and some panels may cause a poor inversion.
In order to avoid such a disadvantage as mentioned above, there are proposals to increase viscosity of the dispersion liquid and prevent the settlement. However, being left to stand for a long period of time, these tend to be too thixotropic, and there is a disadvantage that the yield value and the viscosity of the dispersion liquid after the period of time become higher than necessary.
Furthermore, most of the above-mentioned conventional magnetic display panels use an organic solvent as the dispersion medium. If the dispersion liquid leaks, a problem arises with influence upon a human body and ignition. Such a point is particularly considered as a problem with use of toys and general stationery. Further, it is also concerned about environmental pollution in a manufacturing process etc.
Some documents (for example, Japanese Laid-open Patent No. S53-127032, Japanese Patent Publication No. S59-32796) illustrate that water may be used for the dispersion medium. However, any one of them does not particularly indicate the problem as mentioned above, or offer a particular means for solving the problem, a combination of the thickener, etc., except for the illustration.